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INVESTIGATION OF EXCURSION INSTABILITY IN FORCED CONVECTION IN A VERTICAL HEATED CHANNEL

DOI: 10.1615/ICHMT.2008.CHT.1200
13 pages

Ibrahim Rassoul
Departement D'énergétique Et De Mécanique Des Fluides Faculté De Physique USTHB, B.P. 32, El-Alia, 16111, Alger, Algérie

E-K. Si Ahmed
Departement D'énergétique Et De Mécanique Des Fluides Faculté De Physique USTHB, B.P. 32, El-Alia, 16111, Alger, Algérie

Tewfik Hamidouche
Centre De Recherche Nucléaire d'Alger, 02 Bd Ftantz Fanon, Bp 399 Alger-Gare 16000, Algeria

Abstrakt

Two-phase flows may exhibit unstable behaviour under particular conditions. Nature provides at least an interesting example of such behaviour in geysers which represent highly unstable flow of water and steam.
Two phase flow instabilities have been studied by many researches since flow excursion was first discovered by Ledinegg [1938]. These studies were prompted by potential harmfulness caused by instabilities in large scale nuclear reactor systems. The 1979 accident at Three Mile Island (TMI) reactor proved the importance of the concept of Inherent safety. Two-phase flow instabilities can cause heat transfer crisis, mechanical vibrations, problems with system control, and tube failure. For instance, flow excursion, also known as the Ledinegg instability has received much attention recently. The ongoing research was motivated by the need to establish safe operation margins of the special purpose reactors such as the advanced neutron source reactor (ANSR). The present work focuses on a simulation of pressure drop in forced convection boiling in vertical narrow and parallel uniformly heated channels. The objective is to determine the point of Onset of Flow Instability (OFI) by varying input flow rate. The axial void distribution is also provided. In addition to closure relationships based upon the drift flux model and other constitutive equations are considered to determine the channel pressure drop under steady state boiling conditions. The model validation is performed by confronting the calculations with the Oak Ridge National Laboratory Thermal Hydraulic Test Loop (THTL) experimental data set. Further verification of this model is performed by code-to code verification using the results of RELAP5/Mod 3.2 code. Good agreement is observed, and the prediction of the onset of flow instability at which the minimum point in the demand curve occurs within 12 percent over the all range of experimental results.

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